textproduct: Rapid City

KEY MESSAGES

- Increasingly active convective pattern will develop this week and persist through the upcoming weekend - Slight risk of severe thunderstorms Thursday afternoon/evening, especially west - Saturday could be quite active, but confidence in position of frontal boundaries and upper support/thermal ridge on the low side

UPDATE

Issued at 941 PM MDT Tue Jun 23 2026

Forecast remains mostly on track. Some minor updates to overnight PoPs based on CAMs, have backed off somewhat with only some slight pops in far southwestern SD. PoPs increase in percent and coverage during the day Wednesday as we gain shortwave support. Best chance for any severe storms Wednesday remains in far southwestern SD. Shear remains good all over the CWA, with RAP showing between 50-70kts 0-6km shear during the day. MU CAPE in the 500-1000 j/Kg range during the day will support some thunderstorm development from SW SD into the southern Black Hills and northeast WY. Better updrafts and helicity tracks remain south of the forecast area.

DISCUSSION

(This Evening Through Tuesday) Issued at 1233 PM MDT Tue Jun 23 2026

18z surface analysis had cold front well south/east of the CWA with weak high from MT into western SD. Diurnal heating fluffing some CU here and there per 0.5km visible satellite loop, but atmosphere is short on fuel per 18z KUDX sounding. Better looking south of the CWA. Water vapour loop had upper low over south central Canada supporting west/northwest flow aloft over the northern Plains.

Through tonight, some shra/TS may develop, but best buoyancy south of CWA so not expecting organized convection. Lows tonight will be near guidance.

Wednesday, shortwave moves across MT/Dakotas during peak heating with plenty of shear, but only 500-1000J/kg mean MUCAPE across the far southwest. Isolated severe thunderstorms may occur with the latest CAMS indicating strongest updraft/helicity tracks south of the CWA. Temperatures will remain on the cool side given forecast lower tropospheric soundings.

Thursday looks more interesting as deep upper low/trough drops into southwest Canada/northwest CONUS turning our upper flow west/southwest. Lee trough develops with robust southeasterly return flow over the CWA bringing richer boundary moisture. Barring significant stratus development (guidance/pattern hints this will occur), combination of buoyancy/shear across the western half of the area will be sufficient for a slight risk of severe thunderstorms.

Friday, upper low deepens over the northwest CONUS with southwest flow aloft developing, but with height rises over the northern Plains which may help to suppress organized convection. If something goes, active storms will occur. Saturday/Sunday, upper low ejects northeast with a favorable setup for active/severe thunderstorms each day. Of course, details way too far out to get into, but subjective pattern recognition suggests a busy weekend.

AVIATION

(For the 12Z TAFS Through 12Z Thursday Morning) Issued At 516 AM MDT Wed Jun 24 2026

VFR conditions are expected throughout most of the forecast period. Scattered showers are possible late this morning and afternoon. Low level moisture will increase late tonight with MVFR cigs expected to develop across the far southwest in moist southeast upslope flow toward dawn Thur.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.